"A dirty great big truck with teeth comin' at ya." That's the arresting image someone in Black Water uses to evoke a crocodile attack, and the prospect or experience of such attacks is what the film is all about. It's pretty familiar territory, even without the unfortunate coincidence of the vastly bigger-budgeted Rogue, but for the most part it's handled competently enough.

Sisters Grace (Diana Glenn) and Lee (Maeve Dermody), together with Grace's boyfriend Adam (Andy Rodoreda), embark on a river tour in northern Australia. They've just started to drift through a mangrove swamp when the boat is capsized and their tour guide is summarily dispatched by a saltwater crocodile. Adam and Grace make it to the safety of a tree, while Lee clings to the top of the overturned boat. Eventually she manages to join them up the tree, but their troubles have of course only just begun. They're surrounded by water, and there remains the challenge of venturing forth without becoming reptile food.

The plot drags a bit, and there are implausible moments involving both survival and demise. But most of the acting is quite good and the cinematography is excellent, as is the use of light, especially in a scene involving a lightning storm. In these days of total artifice, you also have to give credit for the use of real crocodiles - albeit subsequently "composited" onto footage of the actors. And there's a great scene with a severed arm. Black Water is, as the tagline says, based on true events. It's also not the stuff that classic horror films are made of, and it's nothing special. But neither is it, shall we say, a crock.